1. Field of the Invention
The present invention relates to a display device, which separately controls a luminance of emitted light for each segment region, and a control method for the same.
2. Description of the Related Art
Most portable terminals such as tablet terminals and smartphones, digital cameras, TVs, and various monitors have liquid crystal display devices (display devices). Liquid crystal display devices comprise: a liquid crystal panel in which a light transmittance is adjustable for each pixel; and a backlight (light source) that irradiates the liquid crystal panel with light.
In recent years, as one of the liquid crystal display devices, there has been known a liquid crystal display device that performs backlight local dimming (hereinafter abbreviated as BLD) control by using a backlight which is capable of separately controlling the luminance of emitted light for each segment region which is obtained by segmenting a display region of a liquid crystal panel into a plurality of pieces. In the backlight, a single or a plurality of light emitting diodes (hereinafter abbreviated as LED) for separately illuminating the respective segment regions is disposed. In addition, the “display luminance” in the present description is a luminance which is measured from pixels (liquid crystal elements) of the liquid crystal panel, and is defined by a product between a transmittance of the pixels and the luminance of emitted light of the LED.
Under the BLD control, in a case where an image includes a dark portion in which a luminance is locally low, and a bright portion in which a luminance is locally high, black floating of the dark part is reduced by decreasing the luminance of emitted light of the segment regions corresponding to the dark portion. Thereby, a contrast ratio of a displayed image, which is displayed in the display region, increases. Therefore, in the liquid crystal display device capable of performing the BLD control (hereinafter simply referred to as a liquid crystal display device), image quality of the displayed image is improved.
In the liquid crystal display device, it is determined whether or not there is a margin capable of an increase in gain (an increase in light transmittance) of pixel values of pixels, for each segment region. In a case where there is a margin, correction is performed such that the luminance of emitted light of the LED is decreased and the gain of the pixel values is increased. For example, in a case where a peak value of the pixel values within the segment region is a ½ of the maximum value allowable in the pixel values, the gain of the pixel value of each pixel within the segment region is increased to twice its original value, and the luminance of emitted light of the LED is reduced to ½ of its original value. Thereby, it is possible to increase the contrast ratio of the displayed image while reducing power consumption.
In the liquid crystal display device that performs the correction, a setting value (hereinafter referred to as a LED setting value) of a luminance of emitted light of the LED is calculated for each segment region. On the basis of this calculation result, light emission of the LED of each segment region is controlled. Here, in the liquid crystal display device in the related art, it is assumed that LED light of a certain segment region does not leak into peripheral segment regions, and under the assumption, the LED setting value is calculated for each segment region. However, it is extremely difficult to realize a liquid crystal display device satisfying the assumption. For this reason, in the liquid crystal display device, in a case where an LED in a single segment region emits light, light emitted from the LED leaks into peripheral segment regions, and therefore it is difficult to set an appropriate LED setting value under the assumption.
Accordingly, in the liquid crystal display device described in JP2007-34251A, contribution percentages of the luminances of emitted light of the LED between the segment regions are calculated in advance, and the LED setting value of each segment region is calculated by solving a simultaneous equation using the contribution percentages.
In the liquid crystal display device described in JP2011-248215A, region coefficients indicating amounts of light leakage between adjacent segment regions are provided in three stages (strong, medium, and weak), for example, and the LED setting value of a certain segment region is corrected with any of the region coefficients having three stages. Consequently, in the liquid crystal display device, by adding up the amounts of light leakage from the peripheral segment regions in a certain segment region, a difference in luminance between adjacent segment regions is reduced.